Method for removably implanting a blood filter in a vein of the human body

ABSTRACT

A method for removably implanting a blood filter in a vein of the human body makes use of apparatus that includes an elastic guide wire onto which there can be fitted a semi-rigid tubular mandrel (itself fitted into a thin-walled tubular sheath). A catheter is provided in the form of an easily divisible flexible tube whose distal end permanently bears the blood filter, and whose proximal end is intended to receive a locating member which will be confined under the skin of the patient. After temporary implanting of the filter, a removable strengthening cable can be inserted in a removable manner in the catheter in order to displace the filter along the sheath during its positioning in a vein, in particular in the inferior vena cava of a patient. This filter can be easily removed after a certain period, when the risks of pulmonary embolism are no longer feared.

This is a continuation of application Ser. No. 07/985,178, filed on Dec.2, 1992, now U.S. Pat. No. 5,300,086, which is a continuation-in-part ofapplication Ser. No. 07/731,536, filed Jul. 17, 1991, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a device for temporarily implanting, in a veinof the human body, and in particular in the inferior vena cava of apatient, a blood filter, and more particularly a blood filter of thetype that is elastically expandable in the radial direction.

The function of blood filters is to hold back the blood clots that mayform in the course of phlebitis or other vascular or cardiovasculardisorders, in order to prevent their migration towards the pulmonaryarteries where they could cause an embolism.

The filters generally used for tilts purpose have the shape of a smallumbrella consisting of a plurality of flexible branches that can beradially expanded. In the rest position (retracted state) the branchesextend approximately parallel to one another and occupy a reduceddimension in the radial direction, and this allows them to be positionedin a vein. Once in place inside the vein, the branches spreadautomatically outward and are immobilized against the wall of the vein,thereby anchoring the filter at the desired site.

Filters of this type are preferably positioned in the inferior venacava, a little below the level of the kidneys.

The equipment that permits positioning of the filter traditionallycomprises a guide rod and a mandrel which make it possible to insert asheath into the vein to the desired depth, in such a way that the end ofthe sheath arrives at the site where the filter is to be positioned.When the filter is positioned in the inferior vena cava, it is known tocarry out the implanting via a percutaneous access route or by"denudation" at the level of the right internal jugular vein. Thepositioning is thus carried out starting from the jugular vein, and viathe superior vena cava. After the sheath is positioned, the mandrel andthe guide rod are withdrawn. The filter is then introduced into thesheath by a special syringe and displaced inside the sheath, along itsentire length, by the mandrel, the latter in this case having the roleof a pusher. When the filter arrives at the free end of the sheath(previously positioned at the desired site in the inferior vena cava),the filter spreads open automatically and anchors in the wall of thevein. The sheath is then removed, and the filter remains permanently inposition.

The main disadvantage of this technique is that the filter can bewithdrawn only by performing a very delicate surgical operation.Unfortunately, the permanent positioning of the filter in the vena cavais a source of complications, in particular, the filter can trigger athrombosis. Moreover, the patient with this filter in place must takeanticoagulant medication for life.

These disadvantages are all the more regrettable since, in a great manyforms of treatment, the positioning of the filter in the vein isnecessary only for a limited period, generally a few weeks or a fewmonths, corresponding to the period during which there is a real risk ofembolism.

For this reason a technique has recently been proposed for implantingthe filter temporarily and removably, so it can be withdrawn after acertain time has elapsed.

For this, the mandrel which is used for implanting the filter ispermanently integral with the latter; after the filter is implanted, themandrel remains inserted in the vein and projects from the body via theaccess route used for the implanting, that is, at the level of the neck,in the region of the jugular vein, when the filter is implanted in thevena cava. Unfortunately, such a rod, which is relatively rigid, is veryuncomfortable for the patient; moreover, because the mandrel projectsfrom the skin, it constitutes a source of infection that may lead toserious complications, especially septicaemia.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the present invention is to overcome the disadvantages ofthe prior art by a new device for implanting a blood filter of the typementioned above, this device being simple to manipulate, use, andimplant reversibly, without the patient being exposed to real risks ofinfection or traumatized by the presence of the implanted devicethroughout the period during which the filter must remain in place.

In the description and claims that follow, the terms "proximal" and"distal" are used with reference to the point on the body of the patientthrough which the blood filter is introduced. According to thisdefinition, the proximal end of an element is that which is nearest thepoint of introduction, and the distal end is that which is furthest awayfrom that point.

The device of the present invention is provided with a locating memberadapted to be disposed subcutaneously for localizing, through the skinof the patient, the catheter to whose distal end the filter is fixed.Especially to avoid infection, the locating member will comprise asleeve of a biocompatible material that encloses an internal closingmeans at the catheter's proximal end. The internal closing means canclose off the catheter.

Further, the apparatus of the present invention will advantageously becomposed of the following elements:

a) an elastic guide wire of small diameter intended to be inserted intothe vein via a percutaneous access route or after denudation;

b) a semi-rigid tubular mandrel capable of being fitted onto the guidewire and displaced along the latter;

c) a thin-walled tubular sheath capable of being fitted onto the mandreland positioned inside the vein by displacing the mandrel along the guidewire;

d) the catheter having the form of an easily divisible flexible tubewhose distal end permanently holds the blood filter;

e) a strengthening cable capable of being removably inserted into thecatheter, thereby making it possible to advance, inside the previouslypositioned sheath, the catheter and its filter in the retracted state,until the latter emerges at the distal end of the sheath and spreadsopen automatically to anchor against the wall of the vein;

f) the locating member, which is thus intended to be fixed at theproximal end of the catheter after removing the strengthening cable andcutting the catheter at the level of the access route.

Furthermore, according to a certain number of advantageous but notrestrictive characteristics:

the proximal ends of the mandrel and of the sheath each bear a head inthe form of a female sleeve that meets LUER international standards. Thehead borne by the mandrel is adapted to butt against the head borne bythe sheath, in order to facilitate their point positioning inside thevein;

the device comprises a tubular syringe body, fitted onto the catheter,that receives the blood filter and holds the latter in the retractedstate;

the proximal end of the head borne by the sheath and the distal end ofthe syringe body are provided with complementary coupling means thatsatisfies the so-called "LUER-Lock" standards, such as athreading/tapping, thereby facilitating the introduction of the filterinto the previously positioned sheath;

the locating member has the form of a sleeve intended to be crimped ontothe catheter;

the locating member is a sleeve free from sharp angles; for example, itmay be ovoid in shape;

the locating member is made of plastic material cast on a deformablemetal ring;

if the deformable metal ring is closely crimped onto the catheter, itcan constitute the above-mentioned catheter proximal-end closing means.Otherwise, a plug inserted into the catheter end through the centralopening of the sleeve can be used as such a closing means;

the catheter is made of plastic material, for example, polyvinylchloride covered with a biocompatible material such as a silicone-basedmaterial;

the distal end of the mandrel bears a radiopaque marker, for example, ametal ring;

the distal end of the catheter, which bears the filter, is also closed.In many cases this feature could be important, since it prevents bloodflowing back into the catheter towards the latter's proximal end.Further, if the catheter is thus closed at both its distal and itsproximal ends, the risk of infection will be further limited.

Briefly slated, the present invention provides a method for removablyimplanting a blood filter in a vein of the human body which makes use ofapparatus that includes an elastic guide wire onto which there can befitted a semi-rigid tubular mandrel (itself fitted into a thin-walledtubular sheath).

A catheter is provided in the form of an easily divisible flexible tubewhose distal end permanently bears the blood filter, and whose proximalend is intended to receive a locating member which will be confinedunder the skin of the patient.

After temporary implanting of the filter, a removable strengtheningcable can be inserted in a removable manner in the catheter in order todisplace the filter along the sheath during its positioning in a vein,particularly in the inferior vena cava of a patient. This filter can beeasily removed after a certain period, when the risks of pulmonaryembolism are no longer feared.

According to an embodiment of the invention, there is provided a methodfor filtering blood within a patient's body by means of an implantableapparatus comprising a filter adapted for filtering blood as itcirculates in a blood vessel and a divisible extension stem implantablewithin the body, the stem having a proximal and a distal end and thefilter is fixed to the distal end, the method includes the steps of,forming an access route to the blood vessel through a skin surface ofthe body. This is followed by introducing the apparatus into the bodythrough the access route with the filter first so as to implant thefilter in the blood vessel. The stem is characterized as having a lengthsufficient to extend along the route.

The method further includes providing a locating member on the proximalend of the stem, with the locating member being adapted to beingdisposed subcutaneously for locating the stem through the skin surfaceof the body; disposing the locating member and the proximal end of thestem subcutaneously in the body in proximity to the access route.

The latter step of disposing includes forming, within the patient's bodyin proximity to the access route, a small space for disposing thereinthe locating member fixed to the proximal end; closing the access route,whereby the locating member, the stem, and the filter remainsubcutaneously disposed in the body.

According to a feature of the invention, there is provided a method forfiltering blood within a patient's body by means of an implantableapparatus comprising a filter adapted for filtering blood as itcirculates in a blood vessel and a divisible extension stem implantablewithin the body, the stem having a proximal and a distal end and thefilter being fixed to the distal end, the method comprising the steps offorming an access route to the blood vessel through a skin surface ofthe body; introducing the apparatus into the body through the accessroute with the filter first so as to implant the filter in the bloodvessel, the stem having a length sufficient to extend along the route.

The of the stem is such that the proximal end thereof extends out of thepatient's body when the filter is introduced into the blood vessel, themethod comprising the further step of cutting the stem at the proximalend before providing the proximal end with the locating member, wherebythe length of the stem is adapted to the length of the access route.

The method further includes providing a locating member on the proximalend of the stem, the locating member being adapted to being disposedsubcutaneously for locating the stem through the skin surface of thebody. Disposing the locating member and the proximal end of the stemsubcutaneously in the body in proximity to the access route, and closingthe access route, whereby the locating member, the stem, and the filterremain subcutaneously disposed in the body.

The above, and other objects, features and advantages of the presentinvention will become apparent from the following description read inconjunction with the accompanying drawings, in which like referencenumerals designate the same elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the various elements constituting the device.

FIG. 2 shows in longitudinal cross-section the distal end of thecatheter fitted with the blood filter.

FIG. 3 is a diagrammatic view illustrating the positioning of the filterin the inferior vena cava of a patient.

FIG. 4 is a longitudinal cross-sectional view of a first embodiment ofthe locating member.

FIG. 5 is a diagrammatic view of the catheter whose proximal and distalends are provided, respectively, with the embodiment of the locatingmember shown in FIG. 4 and with the filter.

FIG. 6 is a longitudinal cross-sectional view of the proximal end of thecatheter to which is fixed a second embodiment of the locating member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The various main elements constituting the device and shown in thedrawings have been given reference numbers as follows: a guide wire 1, atubular sheath 2, a tubular mandrel 3, a catheter 4, a filter 5, astrengthening cable 40, a locating member 7, and a syringe body 6.

Referring to FIG. 1, wire 1 is a wire of small diameter, made, forexample, of metal, which, though elastically flexible, possesses acertain rigidity. Wire 1 has a distal end 10 that is curved to form ahalf loop which gives wire 1 the general appearance of the letter J.

Sheath 2 is a thin-walled, cylindrical tube made of plastic material,for example, polyvinyl chloride. It is open at its two ends. At itsproximal end, it holds a sleeve-shaped head 20, likewise of plasticmaterial, whose diameter is greater than the external diameter of sheath2. Sheath 2 has a certain flexibility. On the free end (proximal side)of head 20 is a threading 200 consisting of one or more threads(LUER-Lock standards).

Tubular mandrel 3 consists of a rod made of semi-rigid plastic materialwhose internal diameter corresponds to the diameter of wire 1, therebyallowing mandrel 3 to be fitted onto wire 1. Mandrel 3's externaldiameter corresponds to the internal diameter of sheath 2, therebyallowing sheath 2 to be fitted onto mandrel 3.

The fitting of mandrel 3 onto wire 1 and of sheath 2 onto the mandrelleaves sufficient play to permit relative longitudinal sliding of thesethree elements.

Tubular mandrel 3 holds at its proximal end a sleeve-shaped head 30 ofLUER standards. Head 30 has a cylindrical or slightly conical extension33 which is adapted to be engaged in a complementary seat provided insheath head 20. After engagement of their respective heads, sheath 2 andmandrel 3 are perfectly integral with one another to such an extentthat, by manipulating only one of the two heads 20, 30, it is possibleto displace the entire assembly of mandrel 3 and sheath 2. Mandrel 3 hasa distal end 32 of a smooth, conical shape with a rounded tip, wherebyit avoids causing trauma during implanting of the device.

At a short distance from end 32, mandrel 3 is provided with a radiopaquemarker 31, consisting, for example, of a small metal ring. The relativelengths of sheath 2 and of mandrel 3 are determined so that, aftercomplete insertion of mandrel 3 into the sheath 2 (with head 30 inabutment against head 20), marker 31 just emerges at the distal end ofsheath 2.

Catheter 4 consists of a very flexible (nonrigid) tube whose externaldiameter is substantially smaller than that of sheath 2. Catheter 4 ismade of a plastic material covered with a biocompatible material such asa silicone based material; the plastic material is, for example,polyvinyl chloride. Mandrel 3 is advantageously made radiopaque, forexample by including particles of barium sulfate in the material ofwhich it is made.

As already mentioned, catheter 4 has a tubular shape, and it can receivein its central lumen a strengthening cable 40 of corresponding diameter,this cable consisting, for example, of a very thin wire of spring steelwound spirally about itself over its entire length.

Referring to FIG. 2, the distal end of catheter 4 is closed by a closureplug 52 which forms part of filter 5. The sliding of strengthening cable40 within catheter 4 (indicated by a double arrow f in FIG. 2) is thuslimited in the distal direction, so that cable 40 serves as a pusherupon introduction of catheter 4, as will be explained below.

Filter 5 is a filter of a known type, of the kind described in theBackground section above. In the embodiment illustrated, filter 5 hasthe form of an umbrella frame which comprises eight branches consistingof thin, flexible, metal strips. There are four long branches 50alternating with four short branches 51 in a uniform angulardistribution of 45°.

Branches 50, 51 are embedded at their proximal ends in closure plug 52of catheter 4. The distal ends of branches 50, 51 are slightly curved topresent a direction essentially parallel to the longitudinal axis XX'both of filter 5 and of catheter 4. It will thus be understood that,when filter 5 is in the unfurled state (as illustrated in the figures),the free ends of branches 50, 51 come to lie correctly against the wallof the vein without risk of trauma to the latter.

Referring again to FIG. 1, the device of the present invention alsocomprises syringe body 6 of plastic material, which has the shape of atubular sleeve able to slide on catheter 4. The length of body 6 isslightly greater than the length of branches 50, 51 of filter 5. Theinternal diameter of body 6 corresponds essentially to the internaldiameter of sheath head 20 and of sheath 2.

The distal end of body 6 is tapped so as to present a threading 60complementary with threading 200 of sheath head 20 in accordance withthe LUER standards.

Referring to FIGS. 4 and 5, locating member 7 comprises a body 70 in theshape of a small sleeve made of flexible plastic material. This sleeve,free of sharp angles, has the general shape of a small olive whose morebulging central part is cast on a metal ring 72.

As is illustrated in FIG. 4 by the arrows g, crimping locating member 7onto a rod previously fitted into a central hole 71 of body 70, andconsequently the fixing of locating member 7 on this rod, can be easilydone by crushing the central zone of body 70 and consequently deformingring 72. As will be seen below, it is thus possible to fix locatingmember 7 at the proximal end of catheter 4 in a simple manner.

We will now explain how the device which has just been describedpositions a blood filter in the inferior vena cava of a human body in areversible manner, it being possible for the filter to be easily removedlater.

The filter is implanted under local anesthesia into a human body,designated H in FIG. 3. In the conventional manner, the surgeon beginsby forming in the neck a percutaneous access route AR in the rightinternal jugular vein JV, or by carrying out denudation.

In a first stage, the surgeon introduces guide wire 1 into the jugularvein. With radiological monitoring, made possible by the radiopacity ofwire 1, the surgeon lowers wire 1 through the jugular vein and to followthe superior vena cava SVC and then the inferior vena cava IVC. Becausedistal end 10 of guide wire 1 is curved, there is no hitching or traumaduring its travel. This operation finishes when distal end 10 hasarrived slightly beyond the zone where filter 5 is to be implanted,generally below the bifurcations of renal irrigation.

The surgeon then makes a small incision for widening on both sides ofthe entry point of guide wire 1, in order to facilitate the operationthat follows.

In a second stage, head 30 being in abutment against head 20, thesurgeon fits onto the proximal end of guide wire 1 (which of courseprojects from the jugular vein) the single assembly consisting ofmandrel 3 and sheath 2. The surgeon lowers this assembly gently alongguide wire 1 until radiopaque marker 31 reaches the zone intended foranchoring filter 5.

In a third stage, the surgeon withdraws guide wire 1 and mandrel 3 fromsheath 2.

In a fourth stage, while syringe body 6 covers filter 5, which isconsequently in the folded-in state, the surgeon connects syringe body 6onto head 20 of the sheath 2 with the aid of complementary threadings60, 200.

In a fifth stage, with strengthening cable 40 situated inside catheter4, the surgeon lowers the catheter 4/cable 40 assembly so that filter 5,still in the retracted state, is transferred first into head 20 and theninto sheath 2. The pushing force applied by the surgeon on the distalend of the catheter 4/cable 40 assembly is transmitted correctly tofilter 5 on account of the strengthening role of cable 40, so thatfilter 5 descends progressively along the sheath 2. This progressivedescent would be difficult in the absence of cable 40 on account of theflexibility of catheter 4 (which is semi-rigid).

When filter 5 has arrived at the distal end of sheath 2, it spreads openautomatically as a result of the flexibility of branches 50, 51, whichcome to bear against the walls of the vena cava at the desired site.This accomplishes the anchoring of filter 5.

In a sixth stage, the surgeon withdraws sheath 2 from the vein.

In a seventh stage, the surgeon withdraws cable 40 from catheter 4 andthen cuts catheter 4 outside the jugular vein, at a short distance fromthe latter. This cutting can be carried out conveniently, for example,using a pair of ordinary surgical scissors, because catheter 4 is easilydivisible.

In an eighth stage, the surgeon fits locating member 7 onto theprotruding proximal end of catheter 4, then fixes locating member 7 bycrimping with the aid of a suitable tool, for example, a pincer.

Finally, the surgeon forms, via the small widening incision, a smallspace under the platysma of the neck, where he tucks in locating member7. The surgeon then closes the access route AR in a conventional manner,in such a way that locating member 7 remains confined under the skinafter suturing. There is therefore no risk of infection by thetranscutaneous route at the level of the neck.

It should also be noted that the fact that catheter 4 is closed at itsdistal end prevents any risk of blood flowing back into catheter 4 inthe direction of the access route. In addition, the crimping of locatingmember 7 onto catheter 4 also seals the latter at its proximal end.

On account of its flexibility, catheter 4 does not in any wayinconvenience the patient nor interfere with the patient's activities.It is completely "forgotten" by the patient throughout the period duringwhich the filter must be kept in position in the inferior vena cava. Theduration of retention of catheter 4 and of filter 5 can range from a fewweeks to several months by virtue of the present invention, in contrastto the only two to three weeks in the prior techniques of temporarypositioning, which posed substantial risk of infection.

It is possible at any given time to check the position of locatingmember 7, either by palpating the skin of the patient or by X-ray. Whenfilter 5 is to be removed, it suffices to reopen the access route AR andto remove filter 5 from the vein by pulling on the end of catheter 4.The special shape of the filter, which can contract freely inward,permits its displacement along the veins IVC, SVC and JV.

The possible principal dimensions of the device are given below purelyby way of indication.

Mandrel 3 and sheath 2 can have a length of the order of 50 to 65 cm;catheter 4, a length of the order of 60 to 80 cm; guide wire 1 and cable40, lengths of the order of 80 to 100 cm.

Guide wire 1 and strengthening cable 40 can have a diameter of the orderof 0.5 to 0.7 mm; mandrel 3 and sheath 2 can have external diameters ofthe order of 3.5 and 4.2 mm, respectively, while catheter 4 can have anexternal diameter of the order of 2 mm. Long branches 50 of filter 5 canhave a length of the order of 40 mm, while short branches 51 can have alength of the order of 25 mm.

After the device is positioned, the effective length of catheter 4, thatis, the length between filter 5 and locating member 7, will generally bebetween 40 and 55 cm.

All the elements constituting the device which is the subject of theinvention are intended to be packaged in one and the same sterilepackaging, for single use, with a view to their sale and delivery tomedical/surgical treatment centers.

It should be clear that other embodiments of a locating member thanthose illustrated in FIGS. 4 and 5 could be used in the presentinvention.

Referring to FIG. 6, one alternative embodiment has a locating member 80that comprises a sleeve 81 made of a soft plastic material (such assilicone) and having a generally rounded external shape with acylindrical front portion 82 that has a circular cross-section. Frontportion 82 is linked to a substantially spherical or ovoid rear portion83.

The two portions of sleeve 81 are coaxially crossed through by a centralaperture 84 wherein is engaged a proximal end 4a of catheter 4. Proximalend 4a is engaged in aperture 84 within front portion 82 to penetratethrough a ring 85 enclosed in sleeve 81 coaxially with aperture 84. Ring85 is deformable, and can be made of metal, so that it can be crimped orclamped with sleeve 81 on proximal end 4a. In this embodiment, proximalend 4a is closed by a plug 86 engaged therein. Plug 86 can consist of ascrew (or its equivalent, such as a notched plug) having an enlargedhead 86a extending into aperture 84 and operable therethrough by anappropriate screwdriver. Of course, locating member 80 will be disposedaround catheter 4 after division thereof, as previously described.

Having described preferred embodiments of the invention with referenceto the accompanying drawings, it is to be understood that the inventionis not limited to those precise embodiments, and that various changesand modifications may be effected therein by one skilled in the artwithout departing from the scope or spirit of the invention as definedin the appended claims.

What is claimed is:
 1. A method for filtering blood within a patient'sbody by means of an implantable apparatus comprising a filter adaptedfor filtering blood as it circulates in a blood vessel and a divisibleextension stem implantable within the body, the stem having a proximaland a distal end and the filter being fixed to the distal end, themethod comprising the steps of:forming an access route to the bloodvessel through a skin surface of the body; introducing the apparatusinto the body through the access route with the filter first so as toimplant the filter in the blood vessel, the stem having a lengthsufficient to extend along the route; providing a locating member on theproximal end of the stem, the locating member being adapted to beingdisposed subcutaneously for locating the stem through the skin surfaceof the body; disposing the locating member and the proximal end of thestem subcutaneously in the body in proximity to the access route; thestep of disposing includes forming, within the patient's body inproximity to the access route, a small space for disposing therein thelocating member fixed to the proximal end; closing the access route,whereby the locating member, the stem, and the filter remainsubcutaneously disposed in the body.
 2. A method according to claim 1,wherein said step of forming an access route includes forming saidaccess route percutaneously.
 3. A method according to claim 1, whereinsaid step of forming an access route includes forming said access routeby denudation of said blood vessel.
 4. A method according to claim 1,wherein said step of disposing includes forming, within said patient'sbody in proximity to said access route and close to said skin surface, asmall space for disposing therein said locating member fixed to saidproximal end, whereby said locating member is detectable by palpationthough said skin surface.
 5. A method according to claim 1, comprising afurther step of detecting said locating member through said skin surfaceby palpation.
 6. A method according to claim 1, wherein said step ofproviding includes at least partially closing said proximal end whileproviding said locating member affixed thereto.
 7. A method forfiltering blood within a patient's body by means of an implantableapparatus comprising a filter adapted for filtering blood as itcirculates in a blood vessel and a divisible extension stem implantablewithin the body, the stem having a proximal and a distal end and thefilter being fixed to the distal end, the method comprising the stepsof:forming an access route to the blood vessel through a skin surface ofthe body; introducing the apparatus into the body through the accessroute with the filter first so as to implant the filter in the bloodVessel, the stem having a length sufficient to extend along the route;wherein the length of the stem is such that the proximal end thereofextends out of the patient's body when the filter is introduced into theblood vessel, the method comprising the further step of cutting the stemat the proximal end before providing the proximal end with the locatingmember, whereby the length of the stem is adapted to the length of theaccess route; providing a locating member on the proximal end of thestem, the locating member being adopted to being disposed subcutaneouslyfor locating the stem through the skin surface of the body; disposingthe locating member and the proximal end of the stem subcutaneously inthe body in proximity to the access route; and closing the access route,whereby the locating member, the stem, and the filter remainsubcutaneously disposed in the body.
 8. A method according to claim 7,wherein the step of introducing includes providing, within the stem, aninner strengthening cable adapted to be removably disposed.
 9. A methodaccording to claim 7, wherein the filter is expandable between a firststate of reduced diameter and a second state of expanded diameter,wherein the stem is a catheter, and wherein the step of introducing theapparatus further comprises:introducing through the access route, aguide wire, the guide wire extending to the blood vessel in which thefilter is to be implanted; introducing around the guide wire anelongated mandrel disposed within an elongated sheath; withdrawing theguide wire and the mandrel from the patient's body; providing thecatheter with an inner strengthening cable adapted to be removablydisposed within the catheter; introducing, into the sheath extending tothe blood vessel, the filter and the catheter, the filter being in thefirst state and the catheter coming after, whereby, when the filteremerges out of the sheath, the filter passes into the second state andbears against the blood vessel; withdrawing the sheath from thepatient's body while leaving the filter in the blood vessel; withdrawingthe strengthening cable from the catheter; and cutting the catheter atthe proximal end, near the skin surface.